PROJECT SUMMARY Emotion dysregulation (ED) increases risk for psychiatric and behavioral problems, and leads to polypharmacy, crisis interventions, and high rates of suicidality. Rates of clinically elevated ED are particularly high among those with autism spectrum disorder (ASD). Effective treatment of ED could greatly reduce morbidity and costs and significantly improve quality of life for individuals with ASD. Unfortunately, the development of evidence- based interventions for ED in ASD has been limited by the absence of measures that assess ED without being biased by differences in intellectual and verbal ability. The Emotion Dysregulation Inventory (EDI) (R01HD079512) was developed to address this obstacle. The EDI is a caregiver report that measures rapidly escalating, intense, and poorly regulated negative emotion and dysphoria. It was validated on 1755 school- aged verbal and nonverbal ASD youth as well as a sample of 1000 youth representative of the general US population. The EDI is already being used in multiple clinical trials and for screening and treatment monitoring in inpatient and outpatient settings across the U.S. and in 10 other countries. This project will build on the EDI's conceptual and psychometric strengths and apply Patient-Reported Outcomes Measurement Information System (PROMIS) methods to develop the EDI-Young Child (EDI-YC for ages 2-5) and the EDI Self-Report (EDI-SR for ages 12+). Samples of 800 participants with ASD, 200 with other intellectual and developmental disorders (IDD), and 1000 from the general community will be recruited to complete calibration and psychometric analysis of each measure using Item Response Theory (IRT) and traditional psychometric analyses. The change-sensitivity of the EDI-YC and EDI-SR will be evaluated in the context of funded clinical trials. The availability of the EDI-YC will motivate ED prevention and intervention in early childhood during this critical period of early brain plasticity. The EDI-SR will be developed through a systematic item refinement process to ensure validity even in the context of cognitive impairments or poor emotional awareness, thereby creating new opportunities to incorporate patient perspectives and include the often overlooked but growing population of adults with ASD or IDD in clinical trials when no caregiver is available. Finally, the translational value of this research will be supported by linking specific neural features of ED (e.g., hypo-activation of the lateral prefrontal cortex (LPFC) during frustration and cognitive inflexibility tasks) to ED in ASD as assessed by the EDI. This will be accomplished through neuroimaging via collection of functional near-infrared spectroscopy (fNIRS) and EDI data in a sample of 125 4- to 17-year-olds with ASD. Because of ED's transdiagnostic significance, the impact will span outcomes from aggression to suicide and other critical symptoms related to ED. We will ensure the EDI battery's utility across populations by evaluating the candidate EDI-EC and EDI-SR items in non-ASD IDD samples, as well as through the generation of general norms from large community samples.